Lighting fixtures typically include a light source that produces a beam of light. The light source may be an illumination source, for example a lamp or bulb, that emits light in many directions, coupled with a reflector that redirects light emitted in an undesired direction into a desired direction. A light source may also be an illumination source that inherently emits light in a desired direction, for example a light emitting diode (LED). A light source may also be an array of illumination sources that inherently emit light in a desired direction, where the illumination sources are arranged to emit light in substantially the same direction or angular range.
A lighting fixture may have a simple illumination optical system that includes only a light source or it may have a more complex illumination optical system that may also include one or more lenses, irises, pattern generators, color filters or other optical elements. Such a complex illumination optical system may provide control of the size, shape, color, contour, pattern, brightness, and other characteristics of the light beam produced by the lighting fixture.
Where a light beam has a size greater than an optical element that is intended to control a characteristic of the beam, an aperture may be used to block portions of the beam. For example, where a circular beam has a diameter larger than the diameter of a lens, an aperture may be used to prevent portions of the beam from traveling past the edges of the lens. Similarly, where a light beam has a size greater than a filtering element, an aperture may be used to prevent portions of the beam from passing the outer edges of the filter. Such unfiltered light could mix with the filtered light, producing a beam having a characteristic different from that of the filter material.
A projection optical system is an imaging system. An imaging system provides a point to point mapping of light from one region of space to another. For example, where the object of an imaging optical system is a digital micromirror device, the optical system is designed to map the light from each pixel to a particular region in the image plane. The order and relative positions of the pixels are preserved in the image plane.
A wash optical system is a non-imaging optical system. A non-imaging optical system conveys light from one region to another, but image formation is not the goal. The designer of a non-imaging optical system is often only concerned with the boundaries of the light emitting and target regions. For example, a non-imaging optical system may map a cylinder of light into a rectangular pattern, as in a car headlamp. An image of the filament structure is not desired, but rather a uniform smear of light. By relaxing the imaging condition, a non-imaging optical system may be designed to be more efficient than an imaging optical system.
The cost of an optical element is typically proportional to its size, with the result that a small aperture is used to prevent a larger light beam from passing around an element made small to reduce its cost. However, a small aperture reduces the energy in the beam by blocking off a portion of the beam. Rather than using an aperture, the size of the beam could be reduced with one or more lenses prior to the beam arriving at the small optical element, but the addition of lenses to an optical system typically increases its length, weight, and cost. Additionally, such lenses can increase the maximum angle of the beam, causing optical aberrations or losses downstream.
The present invention was principally motivated by a desire to address the above-identified issues. However, the invention is in no way so limited, and is only to be limited by the accompanying claims as literally worded and appropriately interpreted in accordance with the Doctrine of Equivalents.